Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
  • H01J37/266—Measurement of magnetic- or electric fields in the object; Lorentzmicroscopy
  • H01J37/268—Measurement of magnetic- or electric fields in the object; Lorentzmicroscopy with scanning beams
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/02—Details
  • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
  • H01J37/05—Electron or ion-optical arrangements for separating electrons or ions according to their energy or mass
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/02—Details
  • H01J37/22—Optical or photographic arrangements associated with the tube
  • H01J37/224—Luminescent screens or photographic plates for imaging ; Apparatus specially adapted therefor, e.g. cameras, TV-cameras, photographic equipment, exposure control; Optical subsystems specially adapted therefor, e.g. microscopes for observing image on luminescent screen
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/02—Details
  • H01J37/244—Detectors; Associated components or circuits therefor
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
  • H01J37/261—Details
  • H01J37/265—Controlling the tube; circuit arrangements adapted to a particular application not otherwise provided, e.g. bright-field-dark-field illumination
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/244—Detection characterized by the detecting means
  • H01J2237/2446—Position sensitive detectors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/244—Detection characterized by the detecting means
  • H01J2237/24485—Energy spectrometers

Definitions

• Electron Energy Loss Spectrometry (EELS) spectrum acquisition in a transmission electron microscope (TEM) exposes a sensor with a spectrum of electrons that have traversed a thin specimen.
• an energy-dispersing device referred to sometimes as a "prism,” which is analogous in effect to an optical prism, which disperses incoming light of mixed frequencies by wavelengths
• EELS electrons of differing energy levels are dispersed by the device by energy level across a detector.
• An EELS device also includes energy shifters after the prism, which can shift the dispersed electron spectrum to expose the image sensor to a desired portion of the full energy spectrum. While a spectrum can be sensed as a one dimensional phenomenon, in EELS, to avoid sensor damage by high energy electrons, a two dimensional pixel array is often used wherein the electron spectrum is typically defocused over multiple pixels in a non-dispersive direction
• Figures 2 and 2A show typical prior art timing of imaging sensor exposure and readout.
• the top chart 210 and close up of the read / reset timing in Figure 2A show the sensor readout periods 211 (time frame R) and periods where there is no read-out 212 (time frame E) timing, with the spectrum height in pixels, s.
• Typical image sensors read-out rows of pixels sequentially. With the sensor oriented such that rows are orthogonal to the y axis, such read-out can be represented as a y-position of the read versus time as is done on the top chart 210.
• rows are typically read out one at a time and then each read-out row is immediately reset, to begin exposure for the next frame. This is an example of a so-called "rolling-read" mechanism.
• Figure 2 A shows a detailed view of the diagonal lines 213 in Figure 2 approximating row reads and resets.
• individual row reads are shown as triangles and row resets as circles. Read operations on each row are followed by a reset of that row.
• the read-out is happening in a region of interest (ROI) or read-out height of a number of rows on the sensor in the y-direction that extends from a y value, or row number of 0 through a y value or row number of s.
• ROI region of interest
• this read-out range can correspond to any ROI in the non-dispersive direction, from a narrow strip to the entire height of the sensor.
• the read-out height is sized to match the height of the spectrum as shown in Fig 1 A.
• Chart 210 also shows periods 212 where there is no sensor read-out process taking place. During these times, the sensor is typically being exposed to a signal such as an EELS spectrum. Periods of exposure without read out enable the sensor to extend the exposure time beyond the time it takes to do one read-out of the sensor.
• the second chart 220 shows timing for a blanking trigger signal (solid line) and the delayed blanking system response (dashed line).
• the bottom chart 230 shows a probe advance trigger signal (solid line) and probe advance system response (dashed line.) In both cases 220 and 230, a delay between trigger signal and response is shown to represent latencies in the system, for instance, time constants associated with reactance of the electron optics being energized in response to the trigger requests.
• sensor readout 211 time frame R
• exposure 212 time frame E
• the signal is read out of the device (charge transfer in the case of a CCD; active pixel readout in the case of CMOS.)
• the duty-cycle spectrum exposure time / total time
• spectrum acquisition rate are therefore both significantly limited when the exposure time is of the order of, or shorter than read-out time.
• the exposure time is approximately the same as the readout time and so duty-cycle in that example is about 50%.
• CCD read-out and common CMOS read-out times are typically of the order of milliseconds (ms).
• the duty cycle tends to zero when spectrum acquisition rate reaches a limit defined by 1/R spectra per second (sps) where R is the sensor readout time and where no exposure time is possible. Commonly this is at around 1000 sps.
• sps 1/R spectra per second
• Known methods to speed up the read-out such as pixel binning in the non-dispersive direction often degrade the signal quality and/or decrease signal-to-noise ratio.
• Figure 1 is diagram of a prior art transmission electron microscope having an electron energy loss spectrometer.
• Figure 1 A is an end-on view of the sensor and deflection plates of Figure 1 illustrating the dispersive and non-dispersive directions for an image of an EELS spectrum.
• Figure 2 is a prior art imaging sensor timing diagram.
• Figure 2A is an enlarged view of the read reset portion of the diagram of Figure 2.
• Figure 3 is an exemplary EELS imaging sensor timing diagram according to an aspect of the invention.
• Figure 3A is an enlarged view of the read/reset/expose portion of Figure 3.
• Figure 4 is a flowchart of an exemplary EELS system according to an aspect of the invention.
• Figure 5 is an exemplary computing system for controlling one or more components of the exemplary system of Figure 1.
• Figure 1 shows an exemplary TEM fitted with an EELS spectrometer, with components that are relevant to the present invention shown.
• An exemplary TEM 110 used with the inventive processes includes a microscope / probe deflector 111 positioned above a specimen 112.
• a spectrometer 120 placed after the specimen includes one or more beam blankers 121, an energy-dispersing prism 122, one or more energy shifters 123, one or more spectrum deflectors 124 and an image-receiving device such as a pixel array sensor 125.
• One or more microcontrollers or computers 126 are connected to and control the deflectors 111, beam blankers 121, energy shifters 123 and spectrum deflectors 124 and are connected as well as to the pixel array 125 to receive the image produced by it.
• Fig 1 A is an end view the sensor 125 of the exemplary device of Fig. 1, in which the energy-dispersive, or x axis for the spectrum runs from bottom to top of the sensor, and the non-dispersive, or y axis for the spectrum runs from left to right.
• Spectrum deflectors 214 are also shown in FIG. 124.
• a two-dimensional imaging sensor such as a charge coupled device (CCD) or active-pixel CMOS sensor
• CCD charge coupled device
• CMOS active-pixel CMOS
• spectrum 129 is typically defocused over multiple pixels in the non-dispersive y-direction. The extent of the y- direction defocus determines the specimen height, marked as "s" on Fig 1 A.
• spectra are obtained from thin samples that yield a strong un-scattered signal, 127, with zero energy -loss and non-zero energy-loss features, such as 128, that rapidly decrease in intensity with increasing energy-loss. After acquisition, the data obtained across height s on the two- dimensional sensor is typically collapsed into one-dimension to yield a plot of signal intensity against energy-loss.
• multiple such spectra are taken in series for different incident positions of electron probes at the specimen 112 to build-up a so-called spectrum image data set (spectrum versus electron probe position).
• spectrum exposure occurs to a first portion of the two-dimensional (2D) imaging array 125 at the same time as read-out of a second portion of the image array.
• the spectrum is deflected in the non- dispersive y-direction at various points in time in synchrony with the read-out. The deflections are performed in a way that ensures the spectrum exposure is always happening on a region of the imaging array that is not being read out.
• An illustrative case is that of a CMOS imaging array using a rolling-read mechanism.
• FIG. 3 A shows row reads 311 and resets 312 for two-and-a-half reads of an ROI of height 2s rows.
• the imaging array is oriented so the slow direction of read is in the y (non- dispersive) direction of the EELS spectrum as shown in Figure 1A.
• rows in the x direction are read one at a time, thus a row read is quick while each successive row is read only after the previous one and, thus, the y direction is relatively slow to be read.
• each spectrum exposure is shifted across the sensor in steps such that the exposed region is never a region that is being simultaneously read-out.
• Figure 3 shows the case where the spectrum position is toggled in the y-direction such that the first half of the sensor (represented by Y axis range from -s to 0) is exposed while the second half (y axis range 0 to +s) is read-out and vice-versa.
• the duty cycle is now only limited by the time it takes to shift the spectrum across the sensor, not by the speed of the read-out.
• the time to shift the spectrum should be a non-exposure time, since the spectrum is not settled in either portion of the imaging array during this time. This time is shown as the sloped portion 343 of the probe system response time in the penultimate chart 341 in Figure 3.
• Top chart 310 of Fig. 3 shows read-out and exposure of an image sensor as a function of sensor array axis y (non-dispersive direction) and time.
• the spectrum height is s pixels
• the read-out time is R
• the exposure time is E.
• Second chart 320 illustrates a beam blanking trigger signal (solid line) and delayed blanker system response (dashed line).
• the third chart down 330 shows the EELS spectrum shift response
• the voltage applied to the spectrum deflectors 124 determines the position of the spectrum in the non-dispersive, y, direction.
• the labels: +V and -V represent a shift of TV, sufficient to shift the spectrum between top and bottom portions of the detector.
• FIG. 3 illustrates two microscope electron probe advance trigger signals (solid lines) and the corresponding probe advance system responses (dashed lines), one set for probe advance every frame 341 and one set for probe advance every other frame 342.
• the delayed system responses represent latencies in the system electronics and electron optics that may cause the system response to lag the relevant signals commanding a relevant change in state.
• the spectrum is shifted in y such that the half of the sensor being read is never the same as the half being exposed.
• the beam is blanked and the spectrum shifted in a time, B.
• the duty cycle is E/(E+B). Typically B « R.
• Figure 4 shows an exemplary process that can be used to perform exposure and acquisition timing as described above for Figures 3 and 3A. Consistent with embodiments described herein, the process of Fig. 4 may be implemented by a TEM EELS system, such as that described above in relation to Fig. 1.
• a TEM EELS system such as that described above in relation to Fig. 1.
• an electron beam is blanked in preparation for deflecting the EELS spectrum to a portion of an imaging array.
• the EELS deflector positions the EELS spectrum toward a first portion of the imaging array (Setting 1).
• the beam deflector can also be adjusted to deflect the probe beam to a new position N on the sample.
• the beam is un-blanked, causing the first sensor portion to be exposed at step 405.
• a second sensor portion is read out and reset at step 406.
• the beam is blanked in preparation for deflecting the EELS spectrum to another portion of the imaging array.
• the EELS deflector positions the EELS spectrum to a second portion of the imaging array (Setting 2).
• the beam deflector can also be adjusted to deflect the probe beam to a new position N+l on the sample.
• the beam is un-blanked, causing the second sensor portion to be exposed at step 411.
• the first sensor portion is read out and reset at step 412.
• the probe position is incremented.
• Figure 5 is a diagram illustrating exemplary physical components of a device 500.
• Device 500 may correspond to various devices within the above-described system, such as microcontroller or computer 126 in FIG. 1.
• Device 500 may include a bus 510, a processor 520, a memory 530, an input component 540, an output component 550, and a
• Bus 510 may include a path that permits communication among the components of device 500.
• Processor 520 may include a processor, a microprocessor, or processing logic that may interpret and execute instructions.
• Memory 530 may include any type of dynamic storage device that may store information and instructions, for execution by processor 520, and/or any type of non-volatile storage device that may store information for use by processor 520.
• Software 535 includes an application or a program that provides a function and/or a process.
• Software 535 is also intended to include firmware, middleware, microcode, hardware description language (HDL), and/or other form of instruction.
• firmware middleware
• microcode microcode
• HDL hardware description language
• these network elements may be implemented to include software 535.
• device 500 may include software 535 to perform tasks as described above with respect to Figure 4.
• Input component 540 may include a mechanism that permits a user to input information to device 500, such as a keyboard, a keypad, a button, a switch, etc.
• Output component 550 may include a mechanism that outputs information to the user, such as a display, a speaker, one or more light emitting diodes (LEDs), etc.
• LEDs light emitting diodes
• Communication interface 560 may include a transceiver that enables device 500 to communicate with other devices and/or systems via wireless communications, wired communications, or a combination of wireless and wired communications.
• communication interface 560 may include mechanisms for communicating with another device or system via a network.
• Communication interface 560 may include an antenna assembly for transmission and/or reception of RF signals.
• communication interface 560 may communicate with a network and/or devices connected to a network.
• communication interface 560 may be a logical component that includes input and output ports, input and output systems, and/or other input and output components that facilitate the transmission of data to other devices.
• Device 500 may perform certain operations in response to processor 520 executing software instructions (e.g., software 535) contained in a computer-readable medium, such as memory 530.
• a computer-readable medium may be defined as a non-transitory memory device.
• a non-transitory memory device may include memory space within a single physical memory device or spread across multiple physical memory devices.
• the software instructions may be read into memory 530 from another computer-readable medium or from another device.
• the software instructions contained in memory 530 may cause processor 520 to perform processes described herein.
• hardwired circuitry may be used in place of or in combination with software instructions to implement processes described herein. Thus, implementations described herein are not limited to any specific combination of hardware circuitry and software.
• Device 500 may include fewer components, additional components, different components, and/or differently arranged components than those illustrated in Fig. 5.
• a display may not be included in device 500.
• device 500 may be a "headless" device that does not include input component 540.
• device 500 may include one or more switch fabrics instead of, or in addition to, bus 510. Additionally, or alternatively, one or more components of device 500 may perform one or more tasks described as being performed by one or more other components of device 500.
• the spectrum read from each region of the sample in a spectrum image remains very pure in the sense that the spectrum obtained at probe position N has no/negligible information from positions N-l, N+l because the electron beam is blanked during both shift of the probe in the microscope and shift of the EELS spectrum to the region of the sensor not undergoing read-out, thus preventing any exposure on the sensor during the slew of the probe between points or slew of the EELS spectrum convolved with the sensor read-out process.
• embodiments described herein can include more movements of spectra across the sensor in the non-dispersive direction than the toggling motion shown in Figure 3.
• the general process would involve N steps with period T, such that a y region equal to the height that can be read-out in time T is exposed at each step.
• the position of the spectrum exposure area would always be some number of steps before the read out of the region.

Applications Claiming Priority (2)

Publications (1)

Family

ID=63245082

Family Applications (1)

Country Status (5)

Families Citing this family (2)

Family Cites Families (7)

• 2018
  • 2018-08-01 US US16/635,725 patent/US11024484B2/en active Active
  • 2018-08-01 EP EP18756093.3A patent/EP3662499A1/de active Pending
  • 2018-08-01 WO PCT/US2018/044786 patent/WO2019028129A1/en unknown
  • 2018-08-01 JP JP2020505186A patent/JP6936915B2/ja active Active
  • 2018-08-01 CN CN201880050477.7A patent/CN111095473B/zh active Active

Also Published As

Similar Documents

Legal Events